City Birds Are Disturbingly More Disheveled Than Country Birds

The “city mouse and the country mouse” is one of those tales (actually, a fable from good ol’ Aesop) that’s ricocheted down the centuries. In the story, the city mouse comes to visit the country mouse and sneers at the simple acorns and wheat stalks meal his host offers, so they head into town for a grandiose, sweetmeat-and-jelly filled dinner – only to get badgered by cats and dogs, depending on the telling. In his Meditations, the Roman emperor-philosopher Marcus Aurelius warned “Think of the country mouse and of the town mouse, and of the alarm and trepidation of the town mouse”; a 13th-century British preacher explained the moral as “I’d rather gnaw a bean than be gnawed by continual fear”; and, according to the Washington Post, just this month, at least one city mouse is making some expansive, heartache-y countrymusic.

Now there’s some empirical validation to that age-old bias to country living, at least in the case of birds. In a small Swedish study, a team lead by Lund University Ph.D. student Pablo Salmón fostered nestling great tits in urban and rural environments. Carried out in April and June of 2013, eight nest pairs were raised in urban nest boxes and 11 in rural nest boxes. When the little birds were 15 days old, Salmón and his colleagues measured the birds’ mass, leg lengths, and took blood samples. They were looking for what happened to telomeres, a part of DNA that’s taken to be a biomarker of aging and fitness. “Telomeres get shorter naturally in each cell replication,” Salmón explained to Science of Us in an email. “However, the attrition rate can be increased in response to external stressors, e.g. infections or inflammatory response.” In just a two-week period, the differences in the birds were significant: Urban nestlings raised in the rural habitat have 11-percent longer telomere length than their siblings in the city. And as the photos attest, while the the country bird is stately, the city bird looks like a streetpreacher.

Salmón and his colleagues say that this is the first time the telomere length in city-versus-country populations has been studied, and he warns that “we have to be careful when extrapolating the results of our study to other species.” This is just one population in a single species, so more research will need to be done to see whether the same pattern happens in other urban areas and with other species. And while there is data on how city life affects humans (the danger-detecting part of the brain is overworked, air pollutants slowly kill us, all that light screws with your sleep) nobody has checked out city-versus-country telomere length. But in the meantime, that weekend away really soundsnice.